Pol Pot (born Saloth Sâr; 19 May 1925 – 15 April 1998) was a Cambodian revolutionary and politician who was the dictator of communist Cambodia from 1976 until his overthrow in 1979. He oversaw mass atrocities and is widely believed to be one of the most brutal despots in modern world history. Ideologically a Maoist and a Khmer ethnonationalist, Pot was a leader of Cambodia's Communist movement, known as the Khmer Rouge, from 1963 to 1997. He served as General Secretary of the Communist Party of Kampuchea from 1963 to 1981, during which Cambodia was converted into a one-party state. Between 1975 and 1979, Pot perpetrated the Cambodian genocide, in which an estimated 1.5–2 million people died—approximately one-quarter of the country's pre-genocide population. In December 1978, Vietnam invaded Cambodia to remove the Khmer Rouge from power. Within two weeks, Vietnamese forces occupied most of the country, ending the genocide and establishing a new Cambodian government, with the Khmer Rouge restricted to the rural hinterlands in the western part of the country.

Born to a prosperous farmer in Prek Sbauv, French Cambodia, Pol Pot was educated at some of Cambodia's most elite schools. Arriving in Paris in October 1949 on an academic scholarship, he later joined the French Communist Party in 1951 while studying at École française de radioélectricité. Returning to Cambodia in 1953, he involved himself in the Khmer Viet Minh organisation and its guerrilla war against King Norodom Sihanouk's newly independent government. Following the Khmer Viet Minh's 1954 retreat into North Vietnam, Pol Pot returned to Phnom Penh, working as a teacher while remaining a central member of Cambodia's Marxist–Leninist movement. In 1959, he helped formalise the movement into the Kampuchean Labour Party, which was later renamed the Communist Party of Kampuchea (CPK). To avoid state repression, in 1962 he relocated to a jungle encampment and in 1963 became the CPK's leader. In 1968, he relaunched the war against Sihanouk's government. After Lon Nol ousted Sihanouk in a 1970 coup, Pol Pot's forces sided with the deposed leader against the new government, which was bolstered by the United States military. Aided by the Viet Cong militia and North Vietnamese troops, Khmer Rouge forces advanced and controlled all of Cambodia by 1975.

Pol Pot transformed Cambodia into a one-party state that he called Democratic Kampuchea, seeking to create an agrarian socialist society that he believed would evolve into a communist one. Year Zero was an idea put into practice by Pol Pot where he believed that all cultures and traditions must be completely destroyed and a new revolutionary culture must replace it starting from scratch. “Year Zero" was announced by the Khmer Rouge on April 17, 1975, where everything before that date must be purged. The Khmer Rouge emptied the cities, frogmarched Cambodians to labor camps and relocated the urban population to collective farms, where mass executions, abuse, torture, malnutrition and disease were rampant. At the Killing Fields, more than 1.3 million people were executed and buried in mass graves. Pursuing complete egalitarianism, money, religion, and private property were abolished and all citizens were forced to wear the same black clothing. Repeated purges of the CPK generated growing discontent; by 1978 Cambodian soldiers were mounting a rebellion in the east.

After several years of violent incursions by the Khmer Rouge on Vietnamese territory resulting in massacres, Vietnam invaded Cambodia in December 1978. By January 1979, Pot and the Khmer Rouge had been toppled. The surviving Khmer Rouge members retreated to the scattered jungles near the Thai border, from where they continued to fight and raid. Severely weakened, they were hunted down by Vietnamese soldiers until their withdrawal in 1989. In declining health, Pol Pot stepped back from many of his roles in the movement. In 1998, the Khmer Rouge commander Ta Mok placed Pot under house arrest. Pol Pot died shortly after.

Taking power at the high point of the communist movement's potency across the world, Pot proved to be divisive to the international communist movement. Many claimed that he deviated from orthodox Marxism–Leninism, but China and the US supported his government as a bulwark against Soviet influence in Southeast Asia. He was widely denounced internationally for his role in the Cambodian genocide and he was also regarded as a totalitarian dictator who was guilty of crimes against humanity.